Aircraft go through phases of flight, commonly, takeoff, climb, cruise, descent and landing. For the takeoff and climb portion of the flight the aircraft engine is required to generate enough horsepower to accelerate and lift the aircraft to altitude. The physics of the problem is that power is needed to accelerate the mass of the aircraft and then once free from the runway additional power is needed to lift the aircraft against the force of gravity. Once at a given altitude and no longer climbing or accelerating the engine need only overcome the drag on the aircraft. This disproportionate power requirement means the aircraft needs to have a large powerplant that can perform the functions of accelerate and climb but then reduce power to that required to maintain level flight.
The amount of power delivered by the typical engine is proportional to its weight. Therefore, an engine capable of getting an aircraft to it's cruise altitude would be heavier than an engine used to maintain level flight. The additional weight of the powerful engine, then must be carried by the aircraft even though it's not yielding power from the additional weight.
An engine that can be both lightweight and powerful would allow this.
Serial Hybrid-Electric Aircraft engines which are a generator to provide power via wires to an electric motor turning a propeller.
Serial Hybrid-Electric Aircraft engines can fail if the generator fails and battery power is lost. Serial Hybrid-Electric Aircraft engines can fail if the circuit between the generator and the propeller motor breaks. Serial Hybrid-Electric Aircraft engines can fail if the motor fails. Serial Hybrid-Electric Aircraft engines can fail if the engine on the generator fails. would be advantageous to provide an aircraft powerplant that can accelerate an aircraft to takeoff speed.
It would also be advantageous to provide an aircraft powerplant that can provide excess horsepower for climb.
It would further be advantageous to provide aircraft powerplant that throttle back to that power necessary for cruise flight.
It would further be advantageous to provide aircraft powerplant that has good fuel economy by operating at maximum efficiency power settings.
It would further be advantageous to provide aircraft powerplant that uses two different sources of power as a backup if one or the other fails.